This invention relates to the field of marine vehicles that are at least partially supported by one or more artificially pressurized air cushions. The air cushion(s) provides a supporting layer of air between the vehicle""s hull and a water surface thereby reducing wetted area friction and hence improving efficiency. There are further benefits when this technology is applied to landing craft since, by regulating the pressurized air supply to the air cushion(s), the draft of the landing craft can be controlled when at a beachhead or when loading vehicles and/or cargo from a supply ship. There are unique advantages to the instant invention related to the method of utilizing loading and unloading ramps that differ from prior art landing craft concepts.
The need for shallow draft high-speed landing craft for military applications is becoming more apparent. The U.S. Navy has developed an amphibious hovercraft called the LCAC (Landing Craft Air Cushion). The LCAC has flexible skirts around its full periphery and is therefore a generic hovercraft in concept. The full 360-degree flexible seals are necessary for an amphibious air cushioned vehicle. The LCAC is capable of speeds of over 40 knots in moderate seas and can transport a 75-ton tank up onto a beach. Propulsion is provided by two 4,000 HP gas turbines driving air propellers. A third 4,000 HP gas turbine provides power to drive the blowers that supply pressurized air to the supporting air cushion(s). To date, approximately ninety LCACs have been built. Cost of each LCAC is over 20 million dollars.
There is also a need for a new class of lower cost non-amphibious high-speed shallow draft landing craft. Because this new class of landing craft is non-amphibious, it does not require the expensive and high maintenance flexible air sealing skirts that extend around the full 360-degree periphery of a hovercraft such as the LCAC. Further, the hovercraft requires air propellers that are noisy and somewhat inefficient at speeds in the 30-60 knot area. The non-amphibious landing craft as proposed herein can utilize more efficient and less noisy water propulsors such as waterjets since its hulls are always in water contact.
The instant invention, called the Air Assisted Landing Craft (AALC) herein, utilizes a blower pressurized air cushioned hull but with fixed hard structure sidehulls. In its preferred embodiment it has a flexible bow seal and a fixed structure stern seal. Some of the unique features of the instant invention include a bow ramp that incorporates means on its underside for attaching a flexible bow seal. When the bow ramp is lowered the flexible bow seal elements simply fold up against the ground. After vehicles and other cargo is discharged onto the beach the bow ramp is retracted to its upper position which places the flexible seals back into position. As the blower(s) is actuated, the air cushion fills with pressurized gas to thereby reduce water draft so that the AALC can back off of the beach.
The instant invention AALC can also incorporate a stern ramp for stern loading and unloading. Since the air cushion stern seal is a fixed part of the AALC structure, it is a further feature of the instant invention to incorporate the AALC""s stern ramp into its air cushion stern seal design This simple stern ramp concept is not possible with standard hovercraft landing craft since they have flexible seals at their stern.
The instant invention offers advancements over Applicant""s earlier inventions as well as over the prior art. These advancements are discussed in some detail in the following sections.
The primary object of the instant invention is to provide a superior landing craft for transporting vehicles and other cargo to beachheads and unloading them safely and easily on said beachheads.
A related object of the invention is that it be capable of operating at high speed where high speed is defined herein as being speeds of over 15 knots.
A further object of the invention is that it be at least partially supported by a pressurized gas cushion.
It is an object of the invention that it can utilize sidehulls to insure transverse or roll stability as well as help seal in the pressurized air cushion(s).
Yet a further object of the invention is that an air or gas cushion stem seal can be a simple part of the hull structure.
It is a directly related object of the invention that the stern seal, in a sum of its parts and as seen in a transverse vertical plane of the hull, be angled over at least a majority of its width.
It is yet another directly related object of the invention that the stem seal be of a generally inverted-V shape.
It is a further related object of the invention that a portion of the stem loading ramp can be recessed into the area of the gas cushion stem seal.
It is a feature of the instant invention that a moveable, in relation to the hull, gas cushion bow seal can be utilized.
It is a directly related object of the invention that the moveable bow seal can be fabricated, at least in part, of a flexible material.
It is a further related object of the invention that the flexible bow seal extend between the sidehulls.
It is a major feature of the invention that the moveable bow seal be, at least in part, attached to a moveable bow ramp so that the moveable bow seal is displaced out of the way when the moveable bow ramp is lowered.
The invention will be better understood upon reference to the drawings and the detailed description of the invention which follow in which: